2019 SUMMER
PROGRAM

Deadline for Applications is
January 31

* denotes the organizer
responsible for participant diversity

Physicists are encouraged
to apply as individual researchers to work
on their own projects for up to five weeks
at any time during the summer. We provide
a serene atmosphere to complete work. The
individual researcher may also choose to
attend any workshop meetings or chat with
other scientists in residence in addition
to working on his or her own research.
Click here for more
information.

The hidden universe ---
encompassing dark matter, dark energy,
inflation, and possible further hidden
sector degrees of freedom --- is one of
the central mysteries in modern
physics. String theory offers a
fundamental perspective on the puzzles
posed by this hidden world. To realize the
potential of this theoretical, top-down
approach, the present workshop plans to
bring together experts in three different
areas: the formal study of the string
theory landscape, the predictions of
string compactifications for cosmology,
and theoretical astrophysics and cosmology
with a focus on dark sectors. Topics
to be discussed include the swampland
program, the signatures of inflation and
reheating in string theory, hidden gauge
sectors, moduli domination, supersymmetry
breaking, and the measure problem.

Current cosmological
observations suggest that we live in a
universe dominated by dark matter and dark
energy while their nature remains elusive.
Compelling evidence for the existence of
dark matter derives from the gravitational
influence exerted on the motions of stars
and galaxies as well as the bending of
light. Meanwhile, finding the dark matter
particle has been challenging due to its
inertness. Despite this, we have a
successful dark matter-based theory of
structure formation in the universe.
Although the theory has been validated
from many independent lines of compelling
evidence, there are a few gaps—a few
observations that challenge the paradigm.
At this juncture a comprehensive
exploration of all possibilities is
warranted, including those that radically
question the current picture to help frame
and refine alternatives. Alternatives to
the dark matter model include
modifications to Newtonian gravity;
generalizations of Einstein’s theory of
general relativity; and extensions to the
standard model of particle physics that
open up an entirely new window—the dark
sector—for the putative dark matter
particle. In this workshop we plan to
discuss the status of the current cold
dark matter picture and the WIMP paradigm;
devising and assessing alternative models
with axions and sterile neutrinos, and
theories; and debating whether and where a
radical rethinking is likely to take us
and how we might be able to test and
verify such alternatives with new
experiments. Taking stock of the
experimental and observational status of
dark matter searches, we will address some
hard questions about current approaches:

At what sensitivity
do nuclear recoil experiments begin to
lose the luster? How do expected
accelerator and astrophysical results
bear on this question? How far should
we push before the WIMP model is no
longer tenable?

What is the right
combination of axion and sterile
neutrino experiments to more fully
probe these candidates? What is
parameter space for viable searches
for these candidates?

Are primordial
black holes of any mass excluded as
the dominant component of dark matter?
How and when can such black holes form
in the early universe and grow without
jeopardizing the ionization history of
the universe?

What can
gravitational waves tell us if
anything about the nature of dark
matter?

What is the right
combination of observations and
astrophysical data that would be
needed to probe new ideas beyond
LambdaCDM?

What role can
simulations play in helping
discriminate between alternate dark
matter models? And what kinds of new
numerical techniques and approaches
would be required to do so?

We intend to hold a
unique inter-disciplinary exploration that
consolidates the current status and
outlines a vision for future work in terms
of experimental, theoretical and numerical
approaches.

Organizers:Marcus Brüggen, University of
HamburgEliot Quataert, University of
California Berkeley*Evan Scannapieco, Arizona State
UniversityEllen G. Zweibel, University of
Wisconsin Madison

Turbulence is
ubiquitous within and around galaxies, as
gravitational instabilities, supernovae,
and feedback from active galactic nuclei
drive supersonic, high-Reynolds number
flows, often threaded by strong magnetic
fields. Recent high-resolution, UV,
optical, infrared, and radio observations
and innovative numerical simulations are
opening up a new window into the complex
evolution of diffuse material over cosmic
time. The program will take
advantage of these advances, bringing
together experts in theory, computation,
and observation to achieve a better
understanding of the life cycle of cosmic
baryons, and the crucial role that
turbulence plays on sub-galactic,
galactic, and intergalactic scales.
Among the specific topics to be discussed
are:

The role of
turbulence in the formation history of
galaxy disks and bulges

The impact of
turbulence in rapidly star-forming
galaxies and its connection to the
driving of galaxy outflows

The physics of
turbulent mixing in the interstellar
and intergalactic media

The role of
hydrodynamic and plasma instabilities
in galaxies and galaxy clusters

The physics of
turbulent dissipation in multi-phase
astrophysical media from hot and
diffuse to cold and dense

Observational
constraints of turbulence in the
intracluster and circumgalactic media

The role of
turbulence in particle acceleration
and magnetic field amplification

June 9
- June 30Active and Driven
Matter: Connecting Quantum and
Classical Systems

Organizers:Aparna Baskaran, Brandeis
University*Silke Henkes, University of
BristolJonathan Keeling, University of
St. AndrewsAditi Mitra, New York University

This program aims to
establish and explore the connections
between two fields: Active matter and
driven quantum matter. Active matter
studies how the paradigms of statistical
physics and hydrodynamics are modified by
the introduction of active elements that
consume energy and do work. Driven quantum
matter refers to quantum systems with
external drives such as optical, THz, or
microwave radiation. Both fields are
focused around the fundamental question of
how sources and sinks of energy modify the
collective behavior, i.e. the statistical
physics, of many coupled elements.
The aim of this meeting is to develop
connections between these fields, in terms
of methods, paradigms of understanding
driven behavior, and classes of problems
that can be addressed. In particular, we
have identified three themes that provide
clear links between the two fields:

Biological systems
consist of collections of cells that work
together to extract energy from their
environments, to survive in stressful
conditions, and ultimately to reproduce or
replicate their basic structures. Complex
cellular processes underlie the
integration of signals from the
environment with the ability of cells to
rapidly respond to changes. Over the last
decade, it has become possible, in diverse
systems from bacteria to human cells, to
study the variability in the genetic
programs at the single cell level. This
has opened the door to a range of new
questions on how single cells process
information, and has led to new conceptual
developments. These include understanding
the role of memory in regulating genetic
networks that respond to stress, the role
of heterogeneity in chemotaxis and
cellular motility, and the relationship
between cell size regulation, cell cycle
progression, and population growth. New
insights are also emerging into the rich
behaviors exhibited by single cells under
fluctuating conditions, where information
processing capacity is intimately related
to long-term survival. The workshop will
focus on common themes in information
processing across a wide range of
biological systems, to enable new
theoretical and quantitative formulations
of biology at the single cell level. These
focal themes are:

Memory and Stochasticity in
Information Processing

Survival Under Stress

Cell Growth, Cell-Cycle Progression,
and Cell Division

July 1
- August 4Realizations and
Applications of Quantum Coherence in
Non-Equlibrium Systems

Higher symmetries appear
in many situations in high energy and
condensed matter theory. They act on
non-local excitations and, like ordinary
symmetries, they may be spontaneously
broken, softly broken, may have 't~Hooft
anomalies, and can be coupled to
background (higher) gauge fields. Higher
symmetries have applications to phases of
quantum field theories, to bosonization in
higher dimensions, and to formulations of
the hydrodynamic theory of strongly
interacting plasmas, among others.
The workshop will cover not only groups,
but also algebras of higher symmetries.
Their structure can be expressed using the
emerging theory of factorization algebras,
which play an important role in some
mathematical approaches to field
theory. Examples include vertex
algebras, which have recently re-emerged
in a prominent role in supersymmetric
gauge theory. We encourage high
energy theorists, condensed matter
theorists, and mathematicians interested
in this area to apply.

The focus of the program
will be on new approaches to quantum field
theory, with a particular emphasis on two
highly active areas: the bootstrap
approach to conformal field theories
(CFTs) and modern on-shell methods for
scattering amplitudes. The two fields are
conceptually related, sharing both
mathematical tools and a philosophical
outlook focusing on physical observables,
and we expect fruitful results to follow
from bringing experts from both camps
together in Aspen for an extended period.
The organizers plan to encourage
communication between participants from
the two main areas by requiring talks to
be aimed at the audience from the other
field and having presentations focused on
explaining potential overlaps in
interests.

The picture of the
electroweak scale that is emerging from
the enormously successful experimental
program at the Large Hadron Collider (LHC)
is becoming ever more clear, yet remains
deeply puzzling. The long shutdown period
following the close of LHC Run 2 in 2018
will be a critical opportunity to reflect
on the lessons learned and opportunities
available for the future. The full
statistical power of the Run 2 dataset
will be valuable for informing the
development of many new directions,
including machine learning, long-lived
particle searches, and the design of
custom detectors. Meanwhile, the
high-energy physics community has also
been revisiting and reimagining common
motivations for physics beyond the
SM. Developing new approaches to the
hierarchy problem, to dark matter, and
establishing the resulting implications
for the search program at the LHC will be
cornerstones of this program. To aid
in the development of a new understanding
of naturalness and map out the long
journey at the energy frontier, this
workshop will gather both theorists and
experimentalists to crystallize and
explore these new ideas.

The direct detection of
gravitational waves by the Laser
Interferometric Gravitational-Wave
Observatory (LIGO) and the European Virgo
detector has opened an entirely new window
to study the Universe. LIGO and
Virgo have uncovered an entirely new
population of binary black holes with
masses up to 30 times that of our Sun, and
the origin of these systems remains hotly
debated. The first discovery of the
merger of two neutron stars in August 2017
was a watershed event for astrophysics,
with associated emission detected across
the entire electromagnetic spectrum.
From just this single binary neutron star
merger we have placed some of the tightest
constraints on the equation of state of
dense material to date, and have
determined that such systems appear to be
the dominant source of heavy “r-process”
elements in the Universe. Our
objective with this workshop is to bring
together astronomers and physicists across
a diverse range of topics to address some
of the most exciting astrophysical
questions that have been raised by these
gravitational wave discoveries, including:
What is the origin of the binary black
hole systems discovered by LIGO and Virgo?
What constraints on the neutron star
equation of state can be derived from
joint gravitational wave and
electromagnetic observations? Are neutron
star mergers indeed the dominant source of
heavy (r-process) elements in the
Universe? The workshop will take
place in the middle of the O3 observing
run, and so should be a timely opportunity
to discuss these topics (and more).

The accelerated
expansion of the Universe is a topic of
great interest to both the physical and
astronomical communities. To settle the
issue whether new physics is required,
we need precise and reliable
measurements of cosmological parameters.
In this era of precision cosmology, the
issue of systematic errors will
ultimately limit our progress in
understanding the nature of dark energy.
Assessment of systematic errors in any
given method is difficult, and therefore
new cosmology tools are needed as a way
to provide independent cross-checks. We
aim at organizing a brain storm meeting
of scientists developing various methods
based on gravitational waves, active
galactic nuclei, gamma-ray bursts,
galaxy clusters imaged in mm and X-ray
band, and strong gravitational lensing.
The workshop will be used to perform two
apparently contradictory tasks:

assignment of the relative
importance of all new tools in the
timescale of the next ten years

collaboration of researchers coming
from different fields in establishing
a reliable and consistent
astro-statistical approach.